Compositions incorporating n-type chalcogenide compositions, particularly chalcogenides incorporating at least cadmium (Cd), have been used in photovoltaic devices as buffer layers in combination with p-type, photovoltaically active, chalcogenide compositions. Illustrative p-type, photovoltaically active chalcogenide compositions often include selenides and/or sulfides of at least one of copper, indium, and gallium, and even more typically at least two of these metals, and even all three of these. Such p-type materials are referred to as CIS, CISS, CIGS, and/or CIGSS compositions (collectively CIGS hereinafter), and the like.
For example, U.S. Patent Application Publication No 2005/0009228 A1 discloses a method for making a heterojunction photovoltaic device to convert solar radiation to photocurrent and photovoltage. The publication discloses the use of a window layer of CdS or an alloy of CdS that contains increased oxygen content. The window layer is deposited by a method that employs a gas mixture of an inert gas and oxygen at or near room temperature. The amount of oxygen used in the gas mixture is from about 1% to about 5% by volume.
U.S. Pat. No. 5,078,804 discloses a thin layer-based solar cell that has a first layer Cu/In/Ga/Se a second layer of Cd/Zn/S, a double layer of ZnO and a metallization structure comprised of a layer of Ni coated with a layer of Al. The Cd/Zn/S layer is deposited by an aqueous solution growth process.
U.S. Patent Application Publication No. 2005/0224111 A1 discloses a layered thin layer semiconductor device that comprises a first transparent layer, a thin second transparent layer that has a conductivity less than that of the first layer, an n-type layer, and a p-type layer. CdS is disclosed as useful in a CIGS or a CdTe photovoltaic device. However, the CdS is deposited by an aqueous process.